The United States on Tuesday announced that tougher rules for labeling Mexican tuna imports as “dolphin-safe” would be expanded to the rest of the world in a bid to end a long-running trade dispute with Mexico.

The World Trade Organization last November upheld a ruling that the United States was discriminating against Mexican tuna imports by applying the tougher catch verification and documentation rules to Mexican fishing fleets in the tropical eastern Pacific Ocean.

Instead of loosening the rules on Mexico, the National Oceanographic and Atmospheric Administration (NOAA) published new rules that raised the standards for all other countries.

“The United States champions policies that protect dolphin populations from fishing practices that endanger them, and today’s announcement of NOAA’s interim final rule is a significant win in that effort,” U.S. Trade Representative Michael Froman said in a statement.

Mexico has been fighting for more than 20 years over rules that it argues have frozen its fishing industry out of a U.S. imported canned tuna market worth $680 million in 2014. Mexico has about a 3.5% share.

Among the largest sources of U.S. canned Tuna imports in 2015 were Thailand, Vietnam, Mauritius, Canada, Ecuador, Fiji, China and Indonesia, according to NOAA’s National Marine Fisheries data.

The clash arose because yellowfin tuna swim with dolphins in the eastern tropical Pacific, where Mexico’s fleet operates, using speedboats to herd the dolphins and large purse seine nets to catch the tuna swimming beneath them.

Millions of dolphins were killed before international conservation efforts set standards to protect dolphins and put professional observers on ships to record each tuna catch.

Mexico argued the agreements had cut dolphin deaths to minimal levels – below the thresholds allowed in U.S. fisheries – and that tuna from other regions did not face the same stringent tests, with ship captains allowed to self-certify that no dolphins were harmed.

But Mexican boats were subject to more paperwork and sometimes government observers to verify that no dolphins were harmed in order to earn a U.S. “dolphin-safe” label.

After the WTO ruling against the United States’ double-standard last year, Mexico earlier this month had requested authority to impose retaliatory tariffs against $472.3 million in imports of U.S. high-fructose corn syrup. The WTO was due to consider these tariffs on Wednesday.

The Humane Society International applauded the expanded verification and documentation rule, saying it “elevates dolphin protections while also insulating the ‘dolphin safe’ label from further challenge.”